An EGR device disclosed in Patent Document 1 (JP 2013-096286, US 2013-0104859) is known as an example of the EGR device that includes a throttle valve generating a negative pressure at an outlet opening of an EGR gas. The EGR device disclosed in Patent Document 1 includes an EGR adjustment valve and a throttle valve in a housing defining therein an intake passage and an EGR passage.
The EGR adjustment valve and the throttle valve of the Patent Document 1 are connected with each other, and a valve unit including the EGR adjustment valve and the throttle valve is downsized so as to meet a requirement for a mountability on a vehicle, a mechanical limitation regarding, for example, a link device, and a requirement for a low-cost manufacturing. Therefore, a distance between the throttle valve and an outlet opening of an EGR passage is short. Consequently, when the EGR gas flows into the intake passage through the outlet opening, the throttle valve may be likely exposed to the EGR gas.
If the throttle valve cooled by an intake air is exposed to the EGR gas with a high temperature and containing water vapor (i.e. moisture generated by combustion), the EGR gas is cooled rapidly, and thus the moisture contained the EGR gas easily adheres to the throttle valve as a condensed water.
The condensed water condensed on the throttle valve is sent downstream of the intake air together with a stream of the intake air. However, when an intake-air compressor of a turbocharger is located in the intake passage which is downstream of the intake air with respect to the throttle valve, the condensed water is drawn into the intake-air compressor, and thus the condensed water may collide with a compressor blade. If the collision of the condensed water with the compressor blade is repeated for a long time, the compressor blade may be partially corroded and eroded.
Moreover, even when the intake-air compressor is not located downstream of the intake air with respect to the throttle valve, the condensed water adhering to the throttle valve flows, and thus a packing, which is made of rubber and provided in the intake passage, may be easily deteriorated by the condensed water W. To take an example, the condensed water adhering to the throttle valve may enter a shaft-inserted hole along a shaft driving the throttle valve. The packing that is made of rubber and fills a gap is provided between the housing and the shaft. Therefore, the condensed water contacting the packing for a long time may cause the packing to be deteriorated, and thus an air leakage may occur.